RNA Interference (RNA i) and RNA Induced Gene Silencing

By

V.Vigneshwaran

madonscience.blogspot.com ADVANCED MOLECULAR BIOLOGY

About RNAi• RNA interference (RNAi) is a system within living cells that takes part in

controlling which genes are active and how active they are. Two types of small RNA molecules – microRNA (miRNA) and small interfering RNA (siRNA) – are central to RNA interference.

• RNAs are the direct products of genes, and these small RNAs can bind to other specific RNAs (mRNA) and either increase or decrease their activity, for example by preventing a messenger RNA from producing a protein.

• RNA interference has an important role in defending cells against parasitic genes – viruses and transposons – but also in directing development as well as gene expression in general.

Discovery • In an attempt to alter flower colors in petunias, researchers introduced additional copies

of a gene encoding chalcone synthase, a key enzyme for flower pigmentation into petunia plants of normally pink or violet flower color. The overexpressed gene was expected to result in darker flowers, but instead produced less pigmented, fully or partially white flowers, indicating that the activity of chalcone synthase had been substantially decreased; in fact, both the endogenous genes and the transgen

• This phenomenon was called co-suppression of gene expression, but the molecular mechanism remained unknown.

• While it was known that plants expressing virus-specific proteins showed enhanced tolerance or resistance to viral infection, it was not expected that plants carrying only short, non-coding regions of viral RNA sequences would show similar levels of protection.

• Craig C. Mello and Andrew Fire’s 1998 Nature paper reported a potent gene silencing effect after injecting double stranded RNA into C. elegans. In investigating the regulation of muscle protein production, they observed that neither mRNA nor antisense RNA injections had an effect on protein production, but double-stranded RNA successfully silenced the targeted gene. As a result of this work, they coined the term RNAi.

RNAi have Won Nobel

Craig C. Mello Andrew Fire

RNAi Induced Gene Silencing in Petunia Plants

The Mechanism of RNA Interference

The long dsRNAs enter a cellular pathway that is commonly referred to as the RNA interference (RNAi) pathway.

First, the dsRNAs get processed into 20-25 nucleotide

(nt) small interfering RNAs (siRNAs) by an RNase III-like enzyme called Dicer.

Then, the siRNAs assemble into endoribonuclease-

containing complexes known as RNA-induced silencing complexes (RISCs), unwinding in the process.

The siRNA strands subsequently guide the RISCs to

complementary RNA molecules, where they cleave and destroy the cognate RNA (

Cleavage of cognate RNA takes place near the middle

of the region bound by the siRNA strand.

Biological Functions Of RNAi

Immunity

Downregulation of genes

Upregulation of genes

Applications• Gene knockdown• Functional genomics• Medicine• Biotechnology

Role of iRNA in Biotechnology…

RNA interference has been used for applications in biotechnology, particularly in the engineering of food plants that produce lower levels of natural plant toxins.

For example, cotton seeds are rich in dietary protein but naturally contain the toxic terpenoid product gossypol, making them unsuitable for human consumption.

RNAi has been used to produce cotton stocks whose seeds contain reduced levels of delta-cadinene synthase, a key enzyme in gossypol production, without affecting the enzyme's production in other parts of the plant, where gossypol is important in preventing damage from plant pests.

Similar efforts have been directed toward the reduction of the cyanogenic natural product linamarin in cassava plants

Role of iRNA in Medicine…

It may be possible to exploit RNA interference in therapy.

A key area of research in the use of RNAi for clinical applications is the development of a safe delivery method, which to date has involved mainly viral vector systems similar to those suggested for gene therapy

Potential treatments for neurodegenerative diseases have also been proposed, with particular attention being paid to the polyglutamine diseases such as Huntington's disease.

RNA interference is also often seen as a promising way to treat cancer by silencing genes differentially upregulated in tumor cells or genes involved in cell division.

Conclusion There are many things on the horizon that Dicer and its RNAi

mechanism may be able to accomplish for us.

ds RNA-based vaccines and/or treatments for viral infections, perhaps including HIV.

Gene silencing of genes in cancer cells.

Treatment of genetic diseases?

More fantastic instances of viral resistance engineered into crops.

References

http://www.ambion.com/techlib/append/RNAi_mechanism.html

http://en.wikipedia.org/wiki/RNA_interference

 http://en.wikipedia.org/wiki/RNA-induced_silencing_complex

http://www.gene-quantification.de/rnai.html

http://www.uni-konstanz.de/FuF/chemie/jhartig/

NOTE: ALL THE IMAGES THAT WERE USED IN THIS POWER POINT SLIDES WERE DOWNLOADED FROM THE GOOGLE IMAGES.

Thank you Vigneshwaran

AUTHOR INFORMATION

By Vigneshwaran V.PhD Scholar, Kuvempu University, INDIA

Follow me at,

https://twitter.com/vvigneshwaran14

https://www.facebook.com/vignesh.waran.7731247

Mail to,vikkku@yahoo.com

YOU COULD ALSO DOWLOAD THE SAME SLIDES FROM :http://madonscience.blogspot.in/

MAD ON SCIENCE